Drilling device and method for producing undercut holes

ABSTRACT

A drilling device for producing undercut holes. The drilling device includes a drilling tool having an axis of rotation and a cutting portion arranged such that the cutting portion drills a hole with a longitudinal axis that is radially offset with respect to said axis of rotation and a centering device operable to apply a lateral force to said drilling tool for moving said axis of rotation towards said longitudinal axis to cause said cutting portion to form an undercut in a said hole.

CROSS REFERENCE TO CO-PENDING APPLICATIONS

This invention claims the benefit of German Patent Application No. 10311 079.8 filed on Mar. 13, 2003, which is hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to a drilling device and method of workingconcrete, brickwork, stone or the like by means of a drilling operationto produce undercut holes.

BACKGROUND OF THE INVENTION

The production of cylindrical drill holes in materials such as concrete,brickwork, stone and the like using various techniques generallyreferred to as “drilling” is common. Often during above-ground,below-ground and street construction, for example, accurately positioneddrill holes are needed, for example, for inserting fastening elements.Provided the holes are simple “passage holes”, the process is relativelysimple, since there are no special requirements on the shape or geometryof the hole, apart from the nominal diameter. Dowel connections on theother hand impose additional requirements on the shape of the drilledhole.

There are already a number of special methods of making so-calledundercut holes for receiving heavy-duty dowel connections. The purposeof these methods is to improve the performance of the hole by shaping itso that the force needed to pull the fastening element out of the holeis increased. This applies in general, but in particular to crackedconcrete. With cracked concrete, it is necessary to prevent the dowelconnection from yielding or subsiding owing to the cracking, which wouldreduce the load-bearing capacity. A positive connection is clearly anadvantage, particularly for filigree elements where there is a limit tothe spreading-apart forces which can be absorbed by the component.

Methods for making undercut holes, based, for example, on German UtilityModel No 8808 256.3 and U.S. Pat. No. 4,993,894, first require thedrilling of a standard drill hole with conventional drilling tools andmachines. Then, in a second operation, by means of a geometrically noteasily definable operation that is frequently called “swivelling orwobbling”, the cylindrical drill hole is widened at its inner end sothat the inner end of an inserted dowel connector can become “wedged” inthe hole. This enables a relatively defined positive connection to bemade with the dowel connector.

Alternatively, there are special tools for making radial grooves in astandard drill hole and thus increasing its lateral roughness. Thesetools are used after drilling in a separate operation requiring a secondworking step. An example of such tools is disclosed in EP 0 795 677.

U.S. Pat. No. 4,989,681 and German Utility Model No 297 15 261 disclosethe asymmetrical insertion of cutting edges, on the assumption that theaxial force (action of pressure) and the cutting angle will result in aneasily reproducible undercut.

In addition there are a number of devices on the market for working withmovable, controlled cutting edges and blades. The difficulty usually isto remove the drilling dust on site and ensure unrestricted use underthe rough conditions found at building sites. These methods and devices,hitherto in hand-guided versions, have not given satisfactory resultswith regard to the requirements of “widening” and “undercutting”, andtherefore have not been commercially successful.

SUMMARY OF THE INVENTION

In an embodiment, the invention provides a drilling device for producingundercut holes, said drilling device comprising a drilling tool havingan axis of rotation and a cutting portion arranged such that it drills ahole with a longitudinal axis that is radially offset with respect tosaid axis of rotation and a centering device operable to apply a lateralforce to said drilling tool for moving said axis of rotation towardssaid longitudinal axis to cause said cutting portion to form an undercutin a said hole.

In another embodiment, the invention provides a method of producing anundercut hole comprising the steps of: drilling a hole with a drillingtool that has a cutting portion arranged to produce a hole having alongitudinal axis that is radially offset with respect to an axis ofrotation of said drilling tool; and applying a lateral force to saiddrilling tool to cause said axis of rotation to move towards saidlongitudinal axis.

In yet another embodiment, the invention provides a drilling device forproducing undercut holes, said drilling device comprising: a drillingtool comprising a drill shaft that defines an axis of rotation of saiddrilling tool and a cutting portion carried at an end region of saidshaft such that, in use, it drills a hole having a longitudinal axisthat is radially offset with respect to said axis of rotation; and acentering device carried by said drilling tool, said centering devicecomprising an elongate member mounted so as to be slidable alongsidesaid drill shaft into said hole to press against said drill shaft andapply a lateral force to said drill shaft, such that the axis ofrotation is moved substantially into line with said longitudinal axis tocause said cutting portion to form an undercut in said hole, and atleast one member connected with said elongate member by which a user ofthe driving device can move said elongate member alongside said drillshaft.

In yet another embodiment, the invention provides a method of producingan undercut hole, said method comprising: drilling a hole with adrilling tool that comprises a drill shaft having an axis of rotationand a cutting head that is positioned such that said hole has alongitudinal axis that is radially offset with respect to said axis ofrotation; maintaining rotation of said drilling tool with said cuttinghead at a predetermined location in said hole and sliding an elongatemember into said hole alongside between said drill shaft and a walldefining said hole to apply a lateral force to said drill shaft andthereby move said drill shaft to bring said axis of rotationsubstantially into line with said longitudinal axis causing said cuttinghead to widen said hole at said predetermined location to form anundercut.

In still another embodiment , the invention provides a drill device forproducing undercut holes, said drilling device comprising: a drillingtool comprising a drill shaft that defines an axis of rotation of saiddrilling tool and a cutter carried at an end region of said drill shaftsuch that, in use, it drills a hole having a longitudinal axis that isradially offset with respect to said axis of rotation; and a centeringdevice operable to apply a lateral force to said drilling tool formoving said axis of rotation towards said longitudinal axis to causesaid cutter to form an undercut in a said hole, said centering devicecomprising: a centering member that is movable from a non-operativeposition outside of said hole to an operative position inside said holein which the member is positioned between said drill shaft and a walldefining said hole so as to provide said lateral force; an operatingdevice connected with said centering member by which an operator canmove said centering member from said non-operative position to saidoperative position; a depth stop device by which a drilling depth ofsaid hole is set; and a control device for said operating device, saidcontrol device being configured to prevent movement of said operatingdevice by which said centering member is moved from said non-operativeposition to said operative position until said drilling tool has drilledsaid hole to said drilling depth set by said depth stop device.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate the presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the invention.

FIG. 1 shows a drilling tool of an embodiment of a drilling deviceaccording to the invention.

FIG. 2 is an enlarged view of the drill head of the drilling tool ofFIG. 1.

FIG. 3 shows a drilling device according to a first embodiment of theinvention incorporating the drilling tool of FIG. 1.

FIG. 4 shows the drilling device of FIG. 3 in a different operatingposition.

FIG. 5 is an enlargement of a portion of FIG. 3 showing the cuttingportion of the drilling tool at the bottom of a drilled hole.

FIG. 6 is an enlargement of a portion of FIG. 4, similar to FIG. 5, butshowing a guide tube of the drilling device at the bottom of the drilledhole.

FIG. 7 shows an undercut hole produced using the drilling deviceillustrated by FIGS. 1 to 6.

FIG. 8 is a view similar to FIG. 3 showing a second embodiment of adrilling device according to the invention.

FIG. 9 is a plan view of a modified guide tube for drilling devicesaccording to the invention.

FIG. 10 is a plan view of an alternative modified guide tube fordrilling devices according to the invention.

FIG. 11 illustrates yet another modification for the guide tube.

FIG. 12 shows yet another modified guide tube fitted to a drilling tool.

FIG. 13 is a view similar to FIG. 3 showing a third embodiment of adrilling device according to the invention.

FIG. 14 shows the drilling device of FIG. 13 in a different operatingcondition.

FIG. 15 is a partial view of the third embodiment showing a possiblemodification.

FIG. 16 shows another form of undercut hole that can be produced bydrilling devices according to the invention.

FIG. 17 shows yet another form of undercut hole that can be produced bydrilling devices according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a drilling tool 2 comprising a drill shaft having means 3for locating the drilling tool in a drive device, such as in a chuck ofa hammer, drill and a conveying screw 4, which, in use, conveys debrisupwardly and out of a hole during a drilling operation. The drillingtool 2 further comprises a drill head 5, and a cutting plate, or blade 6mounted in the drill head. The cutting blade 6 will be made of a hardmetal or other abrasion-resistant cutting material. Such materials willbe well-known to those skilled in the art and will not, therefore, bedescribed in detail herein.

The drilling tool 2 differs from standard drilling tools in that thecutting blade 6 is not symmetrically radially fixed in the drill head 5.Instead, as shown in FIG. 2, the cutting blade 6 is radially offset byan amount “e” with respect to the axis of symmetry, or rotation A, ofthe drilling tool 2.

Referring to FIGS. 3 and 4, a drilling device 7 incorporating thedrilling tool 2 includes a centering device in the form of a guide tube9 fitted on the drill shaft. The guide tube 9 is arranged to be axiallyslidable on the drill shaft and is connected to a laterally projectinghandle 10 by which the guide tube can be moved by an operator. Thehandle 10 projects from a longitudinally extending slot 18 provided inan outer tube, or sleeve, 20 that surrounds the drilling tool 2 andguide tube 9. The slot constrains the movement of the handle 10 so thatthe guide tube 9 can only move axially with respect to the drill shaftand for practical purposes cannot rotate. The outer tube 20 is fitted toa chuck 21 of a drive device, such as, for example, a hammer drill. Thechuck 21 illustrated is an SDS chuck and projects from a body portion 19of the hammer drill in a conventional manner. As is known to thoseskilled in the art, the outer portion of an SDS chuck does not rotate(the drilling tool 2 is rotated by an unillustrated internal part of thechuck. Thus, the outer sleeve 20 does not rotate when the drilling tool2 rotates. A spring 11 is connected to both the handle 10 and the outertube 20 and biases the guide tube 9 to the retracted, non-use, positionshown in FIG. 3.

It will be understood that although illustrated in use with an SDSchuck, the drilling device 7 may alternatively be used with drillingmachines fitted with conventional chucks. In this case, the mounting ofthe outer tube 20 will be such that the chuck can rotate freely and theouter tube 20 does not rotate. It will be appreciated that the outertube 20 can be fitted to a hammer drill (or any other suitable drivemachine that may be used to drive the drilling device 7) in anyconvenient way that provides for non-rotation of the outer tube 20 whilethe drilling tool 2 is freely rotatable.

As shown in FIG. 3, in use, the drilling tool 2 is used to drill into abody, or component, such as a wall 14. As shown in FIGS. 3 and 5, theresult is the production of a conventional plain cylindrical drilledhole 1. As a consequence of the asymmetrical positioning of the cuttingblade 6, the operator will experience unsteady movement of the hammerdrill as drilling is commenced. With reference to FIG. 5, it will beseen that because the cutting blade 6 is radially offset by the amount“e” with respect to the axis of rotation A of the drill shaft, thecentre line B of the hole 1 is offset by the distance “e” with respectto the axis of rotation A.

Once the hole 1 has been drilled to its full depth, as determined by theleading end of the outer sleeve engaging the wall 14, in an immediatelyfollowing step, without switching the hammer drill off or over, theoperator grips the handle 10 and uses it to move the guide tube 9 downthe drill shaft into the drilled hole 1. This is illustrated by FIG. 4.In FIG. 4, the guide tube 9 is shown at its fully extended position atthe bottom of the drilled hole. The guide tube 9 is moved to thisposition by operating the handle 10 and while rotation of the drillingtool 2 is maintained. With the guide tube 9 in this position, radialwidening of the bottom of the hole 1 occurs to produce an undercut 12.

In more detail, when the guide tube 9 is moved in the direction ofadvance 17 (FIG. 4) by use of the handle 10, the asymmetrically fixedcutting blade 6, is gradually forced into a central position therebydriving its radially outermost edge 16 (FIG. 6) into the wall 14 of thepreviously drilled hole 1. Since the edge 16 rotates continuously duringthis movement, it will remove further material from the wall 14 so thata radial widening is automatically obtained to produce an undercut 12 atthe end of the hole 1. FIG. 7 shows the undercut 12 after the drillingtool 2 has been removed.

FIG. 8 shows a second embodiment of the drilling device 7. For ease ofreference, like reference numerals are used to indicate similar oridentical parts. In this embodiment, the outer tube 20 is replaced by agenerally L-shaped support 20 that cooperates with an adjustable depthstop 8. The handle 10 connects with the guide tube 9 via a slot 31 in alimb of the support 20 that extends parallel to the drilling tool 2 andsleeve 9. The slot allows the handle 10 to move axially, butsubstantially prevents rotational movement thereof. Accordingly, theoperator can move the guide tube 9 axially on the drill shaft, butrotation of the guide tube 9 is substantially prevented.

A marking device 30 is carried by the handle 10 and is arranged to markthe part 14 being drilled at a position 32 when the undercut 12 is made.The marking device 30 will only mark the part 14 when the guide tube 9is fully inserted in the hole to produce a fully formed undercut 12. Thedistance moved by the handle 10 to fully insert the guide tube 9 isindicated at 35.

The second embodiment of the drilling device 7 is operated in much thesame way as the first embodiment. That is, a hole 1 is first drilled toa depth determined by the setting of the depth stop 8. The guide tube 9is then slid down the drill shaft while rotation of the drilling tool ismaintained. As before, the insertion of the guide tube centres the drillshaft in the hole, thereby driving the radially outermost edge 16 of thecutting blade into the wall of the drilled hole to produce an undercut,as illustrated by FIGS. 6 and 7. Once the operation is complete, theguide tube 9 is retracted and then the drilling tool 2 is removed fromthe hole, which has been marked as completed by the marking device 30.

The guide tube 9 is a relatively inexpensive part, which in view of theabrasion caused by the drilling dust in the inner wall, will wear.However, by simply releasing the handle 10, it can be quickly replaced,without the need for auxiliary or additional tools.

As illustrated by FIGS. 9 to 12, the external surface of the guide tubemay be relieved to reduce the area of its surface that will contact thewall 14 of the hole 1. FIG. 9 shows a modified guide tube 9 with arecesses 29 defined by a radius 25. At the outer diameter 23 of theguide tube, the extent of the recess 29 is indicated as 26. As shown inFIG. 10, the guide tube 9 may be provided with a plurality of suchrecesses.

In its most basic form, the guide tube 9 is a plain cylinder with a wallthickness 22, outer diameter 23 and inner diameter 24. The provision ofone or more recesses 29 has the advantage of reducing the area of itssurface that contacts the wall 14 of the hole 1 and, in particular, inthe case of brick or stone, provides the advantage of reducing the forceused to insert the guide tube into the hole. The recesses 29 may bedisposed symmetrically (as shown) or asymmetrically about the peripheryof the guide tube 9, as desired.

As illustrated by FIG. 11, the recess 29 may be twisted, or helical,with a pitch angle 28. More than one slanted recess 29 could be providedif desired.

Referring to FIG. 12, the guide tube 9 may be formed by rolling a sheetto form a split sleeve having a longitudinally extending slit 30.Preferably, the slit 30 is twisted at a pitch angle so that the cuttingblade 6 will not jam in the slit during the undercutting operation.

The guide tube shown in FIG. 12 can be used with drilling tools 2 wherethe diameter of the conveying screw part 4 is less than the diameter ofthe locating means 3 such that the sleeve cannot be slid onto the drillshaft over the locating-means 3. Although it is preferable that the slit30 does not run parallel to the axis A of the drill shaft, the slit maybe so-aligned.

In a further, non-illustrated, variation, the guide tube 9 could besurface relieved by perforating the guide tube. Advantageously, theguide tube could be made from a perforated material.

FIG. 13 shows a third embodiment of the drilling device 7 in which, incontrast to the embodiment shown in FIGS. 3 and 4, the depth stop systemis provided inside telescopic outer tubes 42 and 43, which replace theouter tube 20.

FIG. 13 shows the third embodiment in position at the commencement of adrilling operation. For ease of reference, like or similar parts will bereferenced by the same reference numerals as in the previously describedembodiments. In this embodiment the previously described outer tube 20is replaced by a telescopic tube arrangement comprising at least twotubes 42,43. The upper telescopic tube 42 is fastened to the hammerdrill 19 and the lower telescopic tube 43 is connected to the tube 42.The lower telescopic tube 43 is secured to the upper telescopic tube 42by means of a screw 46 that penetrates an elongate slot 45 provided inthe upper telescopic tube. This slot 45 is sufficiently long to permitthe tubes 42,43 to telescope as the drilling tool 2 moves to apredetermined depth defined by stops 47,48. The telescoping movement ofthe tubes 42,43 is made against a spring 45 that biases the lowertelescopic tube 43 to its fully extended position.

The drilling depth is determined by an upper stop 47 and a lower stop 48and by a support ring 38 fixed on the drilling tool 2 in conjunctionwith a second lower stop 49. The supporting ring 38 will typically besecured to the drill shaft by means of a screw or by welding, althoughother means of securement could be used. As shown in FIG. 14, thedrilling tool can be axially fixed at the drilling depth position by anoptional releasable locking means 53. It will be appreciated that inalternative arrangements, the drilling depth may be determined simply bythe stops 47,48 or the support ring 38 and stop 49 alone.

After the drilling depth has been reached, the undercut is made asfollows. The handle 10, previously held in the position shown in FIG. 13by a spring securing device 11 is moved downwards in the slot 18, whichin this embodiment is in the lower telescopic tube 43, pushing the guidetube 9 into the drilled hole. When the guide tube 9 reaches the fullyinserted position shown in FIG. 14, the undercutting operation iscomplete and the volume of structural material removed by theundercutting process can be seen through at least one inspection window50 provided in the lower telescopic tube 43. The opening 50 alsoprovides a means of discharging the volume of drilled material to ensurea fault-free drilling process, even when the dimensions are larger. Itwill be appreciated that in an analogous manner, the outer tube 20 shownin FIGS. 3 and 4 may be provided with one or more apertures.

This manner of operation, shown in FIGS. 13 and 14, avoids numerouscauses of faults during rough operation in a building site environmentassociated with a number of components, such as the depth stop, sinceall of the critical functional elements that have a strong influence onthe overall process are in a protected position inside the twotelescopic tubes 42 and 43 and need not be adjusted relative to oneanother. This is another advantage that increases reliability of thedrilling device.

FIG. 15 shows a modification of the third embodiment, by which theoperator of the drilling device 7 is prevented from moving the guidetube 9 into the hole 1 until the drilling tool 2 has drilled the hole toits full depth, as determined by the depth stops 47, 48 and/or 38/39.

Referring to FIG. 15, the upper, or outer, telescopic tube 42 has aguide member 70 for the handle 10 fitted to it. The guide member 70defines a slot, in which a narrow portion 72 of the handle 10 isreceived (the larger diameter portion of the handle, as shown in FIGS.13 and 14, has been omitted for clarity). The slot has a first elongateportion 74 that extends parallel to the axis of rotation A of thedrilling tool 2 (not shown in FIG. 15) and a second elongate portion 76that is spaced from and extends parallel to the first elongate portion74. The two elongate portions are connected by a transverse extendingconnecting portion 78, which in this example extends perpendicular tothe axis of rotation A. The arrangement of the slot portions 74, 76, 78is such that the slot is generally U-shaped. Although not shown, thecorners of the slot are preferably curved to make movement between theportion 74, 76, 78 smoother.

The slot 18 in the lower, or inner, telescopic tube 43 is aligned withthe second elongate portion 76 and includes a transverse extension 80that extends from the upper end of the slot 18 and is positioned behindthe guide member 70. The transverse extension 80 of the slot 18 extendssufficiently for the narrow portion 72 of the handle to be received inthe first elongate portion 74 while the second elongate portion 76 isaligned with the slot 18 in the lower telescopic tube 43.

FIG. 15 shows the modified third embodiment in the drilling positionillustrated by FIG. 13. In this position, the narrow portion 72 of thehandle is positioned in the slot extension 80 and at the lower end ofthe first elongate portion 74. When drilling of the hole 1 commences,the upper telescopic tube 42 moves downwardly relative to the lowertelescopic tube 43 as indicated by the arrow 82. As this happens, theguide member 70 is also moved downwardly relative to the handle 10 sothat in effect, the narrow portion 72 of the handle approaches the topof the first elongate portion 74, although, of course, the handle doesnot move. The handle is at this stage prevented from moving in the slot18, 80.

When the drilling operation is complete and the full hole depth isreached, the narrow portion 72 of the handle is positioned at the top ofthe first elongate portion 74. The operator can then move the handleacross with the narrow portion 72 of the handle simultaneously movingalong the connecting portion 78 and the slot extension 80. This bringsthe narrow portion 72 of the handle into the upper end of the secondelongate portion 76, which is aligned with the slot 18. The handle 10can then be pushed downwards forcing the guide tube 9 into the hole 1and allowing it to be moved to the position shown in FIG. 14 to form anundercut, as previously described.

It will be appreciated that the length of the first elongate portion 74is such that the narrow portion 72 of the handle is held in the firstelongate portion until the full hole depth (as determined by the stops)is drilled and only then is the handle able to move transversely tobring it into a position at which downward movement of the guide tube 9can commence. Similarly, the length of the second elongate portion 76 issuch that the handle can move the distance necessary to allow the guidetube 9 to be inserted to the desired depth in the drilled hole 1.Preferably, this brings the leading end of the guide tube 9 to aposition just behind, or adjacent to, the cutting blade 6.

It will be understood that further modifications to the principleillustrated by FIG. 15 are possible. For example, the shape of the slotdefined by the guide member 70 could be altered as desired. All that isrequired is that the arrangement of the slot in the guide member 70 andthe slot 18 in the lower telescopic tube is such that the handle 10cannot be operated to move the guide tube 9 into the hole 1 until thefull depth has been drilled. As another example, it is not necessary forthe lower end of the first elongate portion 74 to be open as shown. Thisis merely convenient.

It will be understood that the arrangement shown in FIG. 15 might bemodified to allow for more than one depth setting. In this case, asecond transverse connecting portion (not shown) could branch from thefirst elongate portion (for example in the opposite direction to theconnecting portion 78) to a third elongate portion (not shown).Similarly, the extension 80 of the slot 18 could then extend further inthe same direction to a second slot in the telescopic tube, which wouldbe aligned with the third elongate portion. This could of course bematched to a desired drilling depth with a second drill stop setting.Further modifications would be possible to provide an arrangementsimilar to the gate of an automobile gearbox, so that multiple depthstops could be provided for.

FIG. 16 shows a variation of the radial widening or undercut that can beobtained with a suitably modified cutting blade 6. Similarly, FIG. 17shows another variant of the radial widening or undercut in detail.

The drilling devices illustrated by the embodiments are technicallysimple, but efficient and potentially completely reliable.

It will be appreciated that the embodiments provide a drilling devicethat can produce an undercut hole using a single drilling tool by meansof two steps taken in direct succession, without needing to remove thedrilling tool from the basic hole and without using an additional“special tool”. Therefore, it is not necessary to perform the drillingand undercutting operation as two quite distinct steps involving thechanging of tools or resetting of the machine/drilling device. Thisavoids the need for an additional drilling device and/or an additionalmachine operator and ensures, during rough operation on site, that “nota single hole is forgotten” during “undercutting/widening”, which can bethe case where a second distinct operation is required.

Furthermore, usually the basic drilling operation is accelerated byso-called hammer drilling, i.e. the tool is axially accelerated inrotation by striking mechanisms. With existing systems, hammer drillingduring the undercutting operation must be avoided, and may in practiceresult in occasional faulty operation and failure of the entire system,for example, in a useless hole at a necessarily predetermined position.This may spoil an entire job. The drilling devices of the embodimentscan reliably produce a satisfactory undercut while still hammerdrilling.

In the embodiments, the centering device takes the form of a guide tube9 that is mounted on and is slidable relative to the drilling tool 2. Itwill, however, be understood that this is not essential. The centeringdevice could take the form of one or more elongate members (likefingers) arranged to be insertable into the hole to provide a laterallyacting force on the drilling tool 2 that will move the axis of rotationA towards the hole centreline B. Advantageously, three equispacedfingers could be supported on a collar that could then be connected witha handle in the same way as the guide tube 9.

An advantage of the drilling devices of the embodiments is that theoperation of radially undercutting a drilled hole to provide a positiveconnection for a fixing element (such as a dowel), is performed in astaggered operating sequence in two successive steps with a singledrilling tool. During this process, the cutting portion of the drillingtool does not leave the drill hole, which is advantageous with regard tothe process and organisation. While the hole is initially drilled, thecentering device remains inoperative at the upper end of the drillingtool.

By means of the centering device, which is moved axially downwards alongthe drilling tool and can be in contact with or partially spaced fromthe drilling tool, the offset cutting blade is deflected by apredetermined amount to effect the desired undercut. This cooperation ofthe centering device and drilling tool results in the advantage for theuser of obtaining defined changes in shape or undercut in a singleoperation that is reproducible, reliable and practical.

It will be appreciated that by suitably shaping the outermost edge 16 ofthe cutting blade 6, it is possible to produce undercuts of varyingshape. As shown in FIGS. 7, 15 and 16, the undercut may be plaincylindrical (generally circular in cross-section) or it may be conical.A conical undercut can have sides that taper inwardly towards the bottomof the hole (FIG. 15) or taper inwardly towards the top of the hole(FIG. 16) depending on the shape of the cutting blade. Of course, othershapes are possible.

It will be understood that while the preferred embodiments have beendescribed as separate and distinct embodiments, features of theindividual embodiments can readily be applied to the others to provideyet more embodiments. For example, it would be possible to provide amarking device, for example a colour marking device, with any of theembodiments.

In the embodiments, the guide tube 9 is shown fitted with a handle 10 bywhich the guide tube is moved manually by the drill operator. However,it will be understood that a mechanism could be provided by which theguide tube would be non-rotationally driven by take-off from the chuckdrive.

While the invention is not limited to this, with presently preferredembodiments, the diameter of the drilled hole relative to the wideningproduced by the undercut is substantially in the range 1:1.05 to 1:1.35.Alternatively, a ratio of 1.025 to 1.175 is preferred.

In the preceding description, reference has been made to “upper” and“lower” and “upward” and “downward” movement. It is to be understoodthat this should not be taken as limiting and this language is usedmerely for convenience of description in conjunction with thearrangement as illustrated. It will be appreciated that the drillingdevice can readily be used to drill: upwards, for example into aceiling; transversely, for example into a wall; and downwardly, forexample into a floor.

While the invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the invention, as defined in the appended claims andtheir equivalents thereof. Accordingly, it is intended that theinvention not be limited to the described embodiments, but that it havethe full scope defined by the language of the following claims.

1. A drilling device for producing undercut holes, said drilling devicecomprising: a drilling tool having an axis of rotation and a cuttingportion arranged such that the cutting portion drills a hole having alongitudinal axis that is radially offset with respect to said axis ofrotation; and a centering device operable to apply a lateral force tosaid drilling tool for moving said axis of rotation towards saidlongitudinal axis to cause said cutting portion to form an undercut insaid hole.
 2. The device of claim 1, wherein said centering device isarranged to apply said lateral force to move said axis of rotation to aposition in which it is substantially in-line with said longitudinalaxis.
 3. The device of claim 1, wherein said centering device is axiallyslidable along said drilling tool between a non-operative position andan operative position in which it is received in said hole.
 4. Thedevice of claim 1, wherein said centering device is a tubular membermounted on said drilling tool.
 5. The device of claim 4 wherein saidtubular member is mounted for substantially non-rotational axial slidingmovement relative to said axis of rotation of the drilling tool.
 6. Thedevice of claim 4, wherein said tubular member has an external surfacehaving a surface area and said external surface is relieved to reducesaid surface area.
 7. The device of claim 6, wherein said tubular memberhas a longitudinal axis and said external surface is relieved by atleast one recess therein that extends at an angle to said longitudinalaxis.
 8. The device of claim 1, further comprising a marking deviceconnected with said centering device so as to be movable therewith formarking a surface in which an undercut hole is drilled.
 9. The device ofclaim 1, further comprising a power-assisted mechanism for saidcentering device, said power-assisted mechanism being operable to movesaid centering device relative to said drilling tool to cause saidcentering device to apply said lateral force.
 10. The device of claim 1,further comprising a support device securable to a drilling machine forsupporting said machine against a surface of a part being drilled suchthat said support device engages said surface when the cutting portionis at a predetermined depth in said hole, said support device supportingsaid drilling machine such that said drilling tool is maintained at saidpredetermined depth while said centering device is operated to applysaid lateral force whereby said undercut is formed at said predetermineddepth.
 11. The device of claim 10, wherein said support device isadjustable such that a plurality of said undercuts can be produced atdesired depths in a hole.
 12. The device of claim 10, wherein saidsupport device comprises a telescoping tube arrangement including atleast two telescopic tubes.
 13. The drilling device of claim 1, whereinsaid drilling tool comprises a drill shaft that defines said axis ofrotation and said centering device comprises a sleeve that at leastpartially surrounds a portion of said drill shaft and is axiallyslidable relative thereto, the drilling device further comprising atleast one member connected with said sleeve by which an operator cancause said axial sliding movement of the sleeve for moving the sleeveinto said hole alongside said drill shaft to apply said lateral force tothe drilling tool.
 14. The drilling device of claim 13, furthercomprising a tubular support to be mounted on a drilling machine forsupporting the machine against a surface of a part being drilled atleast when said undercut is being formed, said tubular supportsurrounding said sleeve and defining an aperture and said at least onemember being disposed externally of said tubular support and beingconnected with said sleeve via said aperture, whereby said sleeve can bemoved substantially parallel to said axis of rotation and rotationalmovement of the sleeve is substantially prevented.
 15. The drillingdevice of claim 1, wherein said centering device is mounted forsubstantially axial non-rotational movement relative to said axis ofrotation.
 16. A drilling device for producing undercut holes, saiddrilling device comprising: a drilling tool comprising a drill shaftthat defines an axis of rotation of said drilling tool and a cuttingportion carried at an end region of said drill shaft such that, in use,the cutting portion drills a hole having a longitudinal axis that isradially offset with respect to said axis of rotation; and a centeringdevice carried by said drilling tool, said centering device comprisingan elongate member mounted so as to be slidable alongside said drillshaft into said hole to press against said drill shaft and apply alateral force to said drill shaft, such that the axis of rotation ismoved substantially into line with said longitudinal axis to cause saidcutting portion to form an undercut in said hole, and at least onemember connected with said elongate member by which a user of thedrilling device can move said elongate member alongside said drillshaft.
 17. The device of claim 16, wherein said elongate member ismounted such that the elongate member is substantially prevented fromrotational movement relative to said drill shaft.
 18. A drilling machinefitted with the drilling device of claim
 1. 19. A drilling machinefitted with the drilling device of claim
 16. 20. A method of producingan undercut hole, comprising: drilling a hole with a drilling tool thathas a cutting portion arranged to produce a hole having a longitudinalaxis that is radially offset with respect to an axis of rotation of saiddrilling tool; and applying a lateral force to said drilling tool tocause said axis of rotation to move towards said longitudinal axis. 21.The method of claim 20, wherein said lateral force is applied by slidingan elongate centering device along said drilling tool towards saidcutting portion thereof.
 22. The method of claim 21, comprisingsubstantially preventing rotational movement of said centering devicerelative to said drilling tool.
 23. The method of claim 20, comprisingproviding a support device such that the support device engages asurface of a part being drilled when said cutting portion is at apredetermined depth in said hole and applying said lateral force whensaid support device engages said surface.
 24. A method of producing anundercut hole, comprising: drilling a hole with a drilling tool thatcomprises a drill shaft having an axis of rotation and a cutting headthat is positioned such that said hole has a longitudinal axis that isradially offset with respect to said axis of rotation; maintainingrotation of said drilling tool with said cutting head at a predeterminedlocation in said hole and sliding an elongate member into said holealongside between said drill shaft and a wall defining said hole toapply a lateral force to said drill shaft and thereby move said drillshaft to bring said axis of rotation substantially into line with saidlongitudinal axis causing said cutting head to widen said hole at saidpredetermined location to form an undercut.
 25. The method of claim 24,further comprising substantially preventing rotation of said elongatemember. 26-35. (canceled)